The marginated pencilfish (Nannostomus marginatus) is a small fish that is widely-distributed throughout Guyana and Suriname, plus the middle-to-lower Amazon basin east of the Andes mountains in Peru, Colombia, and Brazil where it inhabits sluggish tributaries, small rivers and swampy areas, particularly in areas with dense growth of aquatic vegetation or submerged woody structures and leaf litter. Typical habitats contain shallow, near still water with very little detectable hardness, a low conductivity, and a pH of 4.0-6.0, with other fishes comprising small characids, other lebiasinids, and dwarf cichlids of the genus Apistogramma. This fish grows to an adult size of just under an inch long. Mature females are noticeably more stocky and rounded and often a little larger than the males.

Marginated pencilfish should be maintained in an aquarium of 10 gallons or larger. A soft, sandy substrate (CS7538) is a good choice. Driftwood (ZM2000) and live or artificial plants may also be incorporated.

Marginated pencilfish prefer a temperature of 72°F to 82°F, a pH of 4.0 to 7.0, and a hardness of 2 to 15°H. Be sure water is clean and well oxygenated.

The marginated pencilfish is a very peaceful fish well suited to a planted aquarium. Good tank mates include small tetras, livebearers, danios, rasboras, cory catfish, loricariid catfish, and dwarf cichlids. Keep them in groups of 6 or more.

Marginated pencilfish are easy to feed fish accepting almost any appropriately sized food offered. In the aquarium they will readily accept flakes (AL165) and small frozen foods. For maximum color, growth, and health these fish will look their best when given probiotics (AL169) in addition to a balanced diet.